Disposable towels, towlettes, and similar sheet products, sometimes referred to as "wipes", have become an increasingly important part of providing for cleanliness in today's society. Whether at home or away from home, traditional cleansing tools such as soap, cloths, and running water may be unavailable, unsuitable, or inconvenient for a particular task. For example, the cleansing of children and infants presents special considerations due to the nature and frequency of the cleansing activity. Often, the use of special agents such as disinfectants an/or moisturizing agents may also be required.
To address these problems, manufacturers of consumer products have developed single-use disposable, synthetic and/or natural fiber-based towel products which are pre-moistened with a nonirritating cleansing agent. As used herein, the terms "single-use" and "disposable" are used interchangeably to refer to towels and packages which are to be used once and then discarded. The terms "moisture", "moistened", and "moistening agent" are intended to refer not only to water or aqueous solutions, but also to any other fluid which may be useful in combination with a towel product. Such fluids may include disinfecting solutions, water-based solutions, oil-based solutions, soaps, lotions, solvents, etc., alone or in combination with dry additives such as powders or granules.
Single-use disposable towel products may be dispensed from a continuous perforated roll, or as discrete towels in a stacked folded arrangement. Stacked and folded towels are preferably interleaved for ease of dispensing. In a folded and interleaved stacked arrangement, discrete towels are interfolded such that they have overlapping edge portions which are substantially parallel to one another, and adhere to one another such that successive towels are fed out through the top of the container, often through an opening sized and configured to hold a leading portion of a towel in an isolated orientation where it can be readily grasped by the user. This method of dispensing is commonly used in multi-sheet containers of dry tissues, such as facial tissues. However, unlike dry sheets, pre-moistened sheets tend to have much higher separation forces; therefore, there is a very narrow range of design parameters such as level of moistness and level of overlap that must be met so as not to cause either the tearing of the topmost towel or the extraction of multiple towels before any separation occurs.
The narrow range of design parameters inherent in interfolded and interleaved pre-moistened towels having overlapping edge portions which are substantially parallel to one another is overcome to a large degree by modifying the geometry of the leading and trailing edges of the sheets. One very acceptable design is disclosed in U.S. Pat. No. 5,332,118, issued Jul. 26, 1994 to Muckenfuhs, which is hereby incorporated herein by reference. The Muckenfuhs towel design utilizes discrete towel sheets in combination with a modified Z-fold stack configuration, the sheets having an overall shape such that the interleaved end edges of adjacent sheets are at least partially non-parallel such that they form an overlapping region having a non-uniform width. This configuration provides improved pop-up dispensing reliability by providing a predictable, repeatable separation process with towel sheets which are pre-moistened or otherwise have an affinity (clinging tendency) toward one another.
The Muckenfuhs towel design, in addition to having an overlapping region having a non-uniform width, may have a region of "underlapping" where there is no overlap of adjacent towels. Consequently, since the amount of overlap at any given point across the sheets determines the shear force required for separation, separation will first occur where the overlap is a minimum and proceed across the overlapping region as a "separation front" moving toward the point of greatest overlap. The separation thus occurs in a predictable fashion, allowing the separation properties of any particular dispensing system to be designed according to a particular application.
The minimal separation forces required to separate adjacent sheets at the point of minimum overlap create special considerations in processing discrete sheets to form a Z-fold stack configuration of wipes suitable for dispensing from a pop-up dispenser. The primary consideration is how to keep positive control and support of the discrete sheets throughout the entire folding, interleaving, and stacking process, thereby maintaining proper sheet-to-sheet positioning. Since such sheets are designed to separate at the point of minimal overlap with relatively low separation forces, positive control and support of the sheets is necessary to minimize shear forces between adjacent sheets during folding and stacking. Positive control and support is particularly desirable in a high-speed, commercially viable production process.
Accordingly, it would be desirable to provide an improved method for preparing discrete sheets and forming them into a stack of folded interleaved sheets.
Additionally, it would be desirable to provide an improved method for preparing discrete sheets and forming them into a stack of folded interleaved sheets where the end edges of adjacent sheets are at least partially non-parallel such that they form an overlapping region having a non-uniform width.
Further, it would be desirable to provide an improved apparatus for forming a stack of folded interleaved sheets from a substantially continuous shingled web of partially overlapping discrete sheets.